The disclosure generally relates to the “active implantable medical devices” as defined by Directive 90/385/EEC of 20 Jun. 1990 of the Council of the European Communities.
This definition includes in particular cardiac implants for monitoring of the cardiac activity and for the generation of stimulation, defibrillation and/or resynchronization pulses, in case of arrhythmia detected by the device, and/or for sensing electrical activity. It also includes neurological devices, cochlear implants, medical substance diffusion pumps, implantable biological sensors, etc.
These devices may comprise a housing generally designated as a “generator”, electrically and mechanically connected to one or more intracorporeal “leads” having electrodes for coming into contact with the tissue (e.g., myocardium, nerve, muscle, etc.) in which it is desirable to apply stimulation pulses and/or to collect an electrical signal.
According to some exemplary embodiments, the present disclosure more specifically relates to a detection/stimulation microlead for implantation in the venous, arterial or lymphatic systems.
The current principle of electrical stimulation of tissues is based on a device, usually called a “lead”, which is an object notably implanted through various venous, arterial or lymphatic vessels, and the function of which is to transmit an electrical signal to the target tissue. The lead may be used to effectuate one or more of the following properties:
Ease of implantation by the physician in a vessel network of the patient, and especially ease of advancing the lead into the vessels by pushing, making the lead follow tortuous branches and crossings, and transmitting torque;
X-ray vision to allow the physician easy navigation through the vessels of the network under X-ray fluoroscopy;
Atraumaticity of the lead in the veins, which requires a very flexible structure and the absence of rigid transition or sharp edges;
Ability to transmit an electrical signal to the tissues and to stably perform monopolar or multipolar electrical measurements;
Biocompatibility with living tissue for a long-term implantation;
Ability to connect to an implantable device, source of signal transmission;
Ability to sterilize (gamma rays, temperature, . . . ) without damage;
Biostability, especially corrosion resistance in the living environment and resistance to mechanical stress fatigue related to patient and organs movement, and
Compatibility with MRI imaging which is particularly important in neurology.
The current architecture of the leads meeting these requirements can be summarized in a generally hollow structure to allow passage of a stylet or a guidewire, and comprising components such as insulated conductor cables, connected to mechanical electrodes for providing electrical conductivity, radiopacity, etc.
These leads thus require a complex assembly of a large number of parts, wires and associated insulation, creating significant risk of breakage due to mechanical stresses to which they are exposed in the long term.
Examples of such leads are given in U.S. Pat. Nos. 6,192,280 A and 7,047,082 A.
Among the difficulties met, the management of stiffness gradients related to mechanical parts used, which strongly affect the implantability properties and mechanical strength over the long term (fatigue), can be cited. Furthermore, in terms of fatigue of assemblies, any stiffness transition zone may induce risks of fatigue, difficulty to sterilize due to the presence of zones difficult to access, and problems of solidity of the conductor junctions at the connection with the electrodes and the connector.
Moreover, the clinical trend in the field of implantable leads is to reduce the size to make them less invasive and easier to handle through the vessels. The current size of implantable leads is typically of the order of 4 to 6 Fr (1.33 to 2 mm).
However, it is clear that reducing the size of the leads increases complexity and imposes technical constraints generating risks.